KR101966416B1 - Method for polishing silicon wafer and method for producing epitaxial wafer - Google Patents

Abstract

The present invention relates to a polishing method of a silicon wafer in which a silicon wafer is subjected to a mirror polishing process, wherein in the mirror polishing process, the silicon wafer is annealed and thereafter the surface of the silicon wafer is treated with ozone gas or ozone water There is provided a polishing method for a silicon wafer which performs a treatment for removing metal impurities adhering to the surface of a silicon wafer by an oxidation treatment and an oxide film removing treatment using a hydrofluoric acid vapor or an aqueous solution of hydrofluoric acid to perform finish polishing. This makes it possible to prevent PID from occurring in the silicon wafer by the mirror polishing process and to prevent deterioration of the surface quality of a silicon wafer after the mirror polishing process or an epitaxial wafer obtained by laminating an epitaxial layer in a subsequent process A method of polishing a silicon wafer and a method of manufacturing an epitaxial wafer are provided.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method of polishing a silicon wafer and a method of manufacturing an epitaxial wafer,

The present invention relates to a polishing method of a silicon wafer and a method of manufacturing an epitaxial wafer.

It is known that the unevenness of the epitaxial layer generated in the epitaxial growth process of the semiconductor silicon wafer is derived from scratches or PID (Polishing Induced Defect) generated in the mirror polishing process as the previous process.

The scratches on the wafer after the mirror polishing involve dislocations, which are crystal defects. Furthermore, when epitaxial growth is performed on the wafer on which the scratches are introduced, dislocations propagate to cause a dislocation in the epitaxial layer, and the quality of the epitaxial layer also deteriorates. From this, it is important that the wafer before epitaxial growth after mirror polishing is a wafer free from scratches.

Fig. 7 shows epitaxial defects in the epitaxial layer which are generated when epitaxial growth is performed on a wafer (polished wafer) after mirror-polished, in which deformation such as scratches remains. The enlarged view of the lower left corner shows a state where deformation is present in the vicinity of the interface between the epitaxial layer and the substrate.

On the other hand, when epitaxial growth is performed on the PID, it is confirmed that convex portions (projections) reflecting the shape of the PID are generated on the outermost surface of the epitaxial layer. Also, it can be confirmed that there is no defect such as dislocation in the epitaxial layer immediately under the convex portion, and it is an epitaxial layer which does not disturb crystallinity.

8A is an image obtained by observing a PID on a polished wafer with a laser microscope (MAGICS manufactured by Lasertec Corporation), and FIG. 8B is a view showing the relationship between the triboelectric point It is an observation image. As shown in the image after the epitaxial growth, the projection due to the PID can be seen.

Fig. 9 shows the result of performing epitaxial growth on the wafer whose PID was confirmed, and observing the cross-section of the convex epitaxial layer observed at the tie point with the PID by TEM. The epitaxial layer is defect-free. It is found that only the outermost surface of the epitaxial layer has a convex shape over a width of 200 nm, and the height thereof is about 2 to 3 nm.

In the prior art, defects in flaw aggregation can be reduced by sufficiently securing the amount of cutting in mirror polishing.

On the other hand, with respect to the PID, a main method is to sufficiently manage and then reduce the polishing apparatus and the polishing cloth by using various methods such as Patent Document 1 and the like. In the prior art for PID, it is also possible to carry out the cleaning as in Patent Document 2 immediately before the epitaxial growth after the mirror polishing.

Japanese Patent Application Laid-Open No. 2008-205147 International Publication No. 2010/150547

As described above, conventionally, the same techniques as those of Patent Documents 1 and 2 are adopted as the PID countermeasures, but it is insufficient to prevent the deterioration of the surface quality of the polished wafer and the epitaxial wafer on which the epitaxial layer is formed.

Therefore, the present inventor investigated the PID.

First, by performing SEM (Scanning Electro Microscopy) observation and EDX (Energy Dispersive X-ray spectroscopy) analysis on the PID existing on the surface of the silicon wafer subjected to mirror polishing after slicing the silicon ingot and performing grinding or the like A peak of the generated X-ray representing the metal was detected from the PID portion.

In the example shown in Fig. 3 (A), Zr (2.042 keV) of metal impurities was detected in addition to silicon. In the example shown in Fig. 3B, Ni (0.851 keV) of metal impurities was detected.

Also, when the same analysis was carried out at a portion of scratches and scratches, a metal peak was obtained in the same manner.

Ni of metal impurities was detected in the scratches shown in Fig.

Further, the PID was further investigated, and the cross-sectional structure of the PID was observed by TEM. As a result of EDX analysis, it was clear that among the total height of PID of 3 to 6 nm, about 2 nm of the upper layer was the metal deposit.

5 (A) is an SEM image of a PID, FIG. 5 (B) is a cross-sectional TEM observation image of the PID, and FIG. 5 (C) is an enlarged view thereof. 5 (D) shows the result of the EDX analysis of the surface portion of the PID. As in the EDX analysis results, Zr was detected in the surface layer portion of the PID.

In addition, the metal species detected by irradiation were Fe, Ni, and Zr.

These are consistent with the results of the analysis of the grinding stone components and the analysis of the abrasive grains. Table 1 shows the composition analysis of the grinding wheel.

[Table 1]

The mechanism of attaching the above-described metal impurity to the PID is presumed as follows. The outline of this mechanism is shown in Fig.

First, silicon single crystals are sliced into wafers using a wire saw. In this step, the processing damages are introduced into the wafer by the abrasion of the slice wire and the slurry and the pressure thereof.

Then, after cleaning, etching is performed with an acid or an alkaline solution to remove processing damage, and the introduced damage is forcibly removed. In this case, not all of the damage is removed, or cracks such as cracks introduced at the time of slicing are not removed.

Thereafter, the grinding by the grinding wheel or the abrasive grains, or the removal of the residual deformation by the wraps or the wraps is performed. In the above-described process, there is a deformation to be removed, while a new deformation is introduced. As a result, the residual deformation introduced by the slicing process and the deformation introduced by grinding or lap remain as a composite deformation. After cleaning, it is sent to the next process.

When the metal impurities are introduced into the gap of the composite deformation and the residual deformation is removed by the next polishing step, if metal impurities appear on the surface layer, the polishing amount ), Resulting in a PID.

In general, the metal impurities may be removed in various cleaning processes. However, the present inventor has foreseen that, depending on the slight gap of the introduced deformation or the structure thereof, sufficient purification of the cleaning solution does not occur and the removal of the metal impurities is not performed. It can also be deduced from the detection of Ni from scratches on the wafer surface in past SEM-EDS analysis examples.

Here, for example, in the cleaning method after the mirror polishing process of Patent Document 2, the PID itself may be removed, but a concave shape is formed on the surface of the wafer after removal. Depending on the concave shape, there is a possibility of causing an epitaxial defect accompanied with dislocation in the subsequent epitaxial growth step. Therefore, the cleaning method of Patent Document 2 is insufficient as a PID countermeasure as described above.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing a semiconductor device, which can prevent PID from occurring in a silicon wafer by a mirror polishing process, And a method of manufacturing an epitaxial wafer, which can prevent deterioration of the surface quality of the epitaxial wafer.

Removal can be forced out of the process system.

Therefore, in the subsequent finish polishing, there is no hardness difference between the silicon and the metal on the surface of the silicon wafer, which is a cause of generation of the PID, so that the finish polishing can be performed uniformly. Accordingly, no PID is present, and a polished wafer of flat and high quality can be produced.

Further, since such a high-quality polished wafer can be obtained, when an epitaxial layer is laminated in a later step, a projection due to PID does not occur on the surface, and an epitaxial wafer having excellent surface quality can be obtained.

Further, RCA cleaning can be performed on the silicon wafer subjected to the metal impurity removal treatment.

In this way, organic particles and metal particles on the surface of the wafer can be removed.

Further, the silicon wafer subjected to the above finish polishing can be finishing washed.

In this way, various particles existing on the surface of the wafer after the finish polishing can be removed.

Further, the present invention provides a method for manufacturing an epitaxial wafer, characterized in that an epitaxial layer is formed on the surface of a silicon wafer subjected to a mirror polishing process by the above-described method for polishing a silicon wafer.

With this epitaxial wafer manufacturing method, an epitaxial layer can be formed on a polished wafer in which the generation of PID is suppressed, so that it is possible to obtain an epitaxial wafer excellent in surface quality in which the occurrence of projections due to PID is suppressed.

As described above, according to the present invention, it is possible to obtain a flat, high-quality polished wafer which can remove metallic impurities adhering to the surface of a silicon wafer in a mirror polishing process and suppress the generation of PID after finish polishing . Further, it is possible to obtain an epitaxial wafer having excellent surface quality, in which the occurrence of projections due to PID is suppressed.

Fig. 1 is a flow chart showing an example of a processing step in a polishing method of a silicon wafer and a method of manufacturing an epitaxial wafer according to the present invention.
Fig. 2 is a result of surface inspection of a silicon wafer, a polished wafer, and an epitaxial wafer after rough polishing in Examples and Comparative Examples.
3 is a measurement chart showing an example of the peak of the generated X-ray showing the metal from the PID part. (A) Zr detection example, (B) Ni detection example.
4 is a diagram showing an example of a scratch and an example of a peak of a generated X-ray showing metal (Ni) from a scratch.
5 is (A) SEM image of PID. (B) is a cross-sectional TEM observation of the PID, and (C) is an enlarged view thereof. (D) EDX analysis result of the surface part of the PID.
Fig. 6 is an explanatory diagram showing the outline of a mechanism in which metal impurities are attached to the PID.
7 is an observation chart showing an example of an epitaxial defect in the epitaxial layer.
8 is (A) an observation view of a PID on a polished wafer. (B) is an observation view of protrusions at a tie point when epitaxial growth is performed.
9 is a cross-sectional view of a convex epitaxial layer observed at a tie point with the PID by carrying out epitaxial growth on a silicon wafer whose PID has been confirmed.

Hereinafter, the present invention will be described in detail with reference to the drawings as an example of an embodiment, but the present invention is not limited thereto.

The inventors of the present invention have conducted intensive studies on the PID of the silicon wafer surface. As a result, metal impurities are introduced into the composite deformation caused by the slicing process, the grinding and lapping process, etc., and when the complex deformation is removed in the mirror polishing process, there occurs a difference in the amount of polishing due to the hardness difference between the metal and silicon, .

In addition, for example, in the cleaning method as in Patent Document 2, a concave shape is formed in the polished wafer after cleaning, causing an epitaxial defect accompanied by dislocation in the subsequent epitaxial growth step, which is insufficient for the PID countermeasure .

Therefore, the inventor of the present invention has found that, when the metal impurity is removed by performing treatment using ozone gas or the like after the rough polishing, finishing polishing is performed to suppress generation of PID and to provide a polished wafer having high surface quality An epitaxial wafer can be obtained, and the present invention has been completed.

Fig. 1 is a flowchart showing an example of processing steps in a polishing method of a silicon wafer and a method of manufacturing an epitaxial wafer of the present invention.

(Slicing process)

A silicon ingot manufactured by the Czochralski method is sliced on a wafer by a wire saw.

(Grinding and lapping process)

The obtained slice wafer is etched to remove the process damage, and then the grinding process or the lap process or both of these processes are performed.

In addition, before and after these steps, cleaning can be carried out as needed. For example, as shown in Fig. 1, RCA cleaning can be performed after the grinding and lapping process. As a result, organic particles and metal particles on the surface of the wafer can be removed.

(Mirror Surface Polishing Process)

<Abrasive polishing>

Then, the mirror polishing process is performed. In this mirror polishing step, the abrasion is first performed.

In the rough polishing, for example, a polishing cloth attached to a rotatable platen and a silicon wafer supported on a wafer holding plate of a polishing head are polished by contact with an appropriate pressure. At this time, an alkali solution containing colloidal silica (abrasive slurry, abrasive, etc.) is used. By adding such an abrasive to the contact surface between the polishing cloth and the silicon wafer, the polishing slurry and the silicon wafer cause a mechanical chemical action and the polishing proceeds.

As the polishing apparatus, any one of a double-side polishing apparatus and a single-side polishing apparatus may be used. In addition, various conditions such as the composition of the polishing slurry, the temperature, the polishing pressure, the polishing rate, and the polishing rate are not particularly limited.

Furthermore, as this rough polishing, not only single-stage polishing but also plural-stage polishing can be performed. For example, the secondary polishing may be divided into two steps, and the secondary polishing may be performed stepwise by using abrasive or polishing cloth having a smaller scale than primary polishing.

<RCA cleaning, pure cleaning>

After performing the above-described coarse graining, the organic particles and metal particles on the wafer surface are removed by RCA cleaning. Thereafter, rinsing with pure water is performed (pure washing). The rinsing process may be either an overflow method using an immersion fluid used in a batch method or a jetting method.

<Treatment with hydrofluoric acid, pure water>

Then, the silicon oxide on the surface of the wafer is removed by dipping or spraying an aqueous solution of hydrofluoric acid in the hydrofluoric acid aqueous solution. The concentration of the aqueous solution of the hydrofluoric acid solution may be, for example, about 1 to 5%, and is not particularly limited to this concentration. In order to effectively prevent the adhesion of new particles from being promoted because the hydrofluoric acid concentration is higher than necessary, it is preferably 5% or less. The immersion time in the aqueous solution of hydrofluoric acid or the time of spraying of the aqueous solution of hydrofluoric acid can be changed according to the concentration. As a standard, for example, the time for the surface of the silicon wafer to become water repellent can be set. Since the adhesion of the particles is promoted as the immersion time or the injection time is increased, it is preferable to set the particle size to a minimum such that water repellency is ensured.

Thereafter, pure water is rinsed, and the silicon wafer is dried by spin drying, IPA drying, or the like.

<Metal impurity removal treatment>

Then, a process of removing metal impurities adhering to the surface of the silicon wafer is performed.

Here, a description will be given of a case where oxidation treatment using ozone gas (ozone water) and oxidation film removal treatment using an aqueous solution of hydrofluoric acid (hydrofluoric acid vapor) are described.

First, after the above-described rough polishing, the surface of the cleaned silicon wafer is oxidized using ozone gas. At this time, on the surface of the silicon wafer, a portion where metal impurities buried in the composite deformation, scratch, or micro crack is adhered is included, and silicon is forcibly oxidized to form a silicon oxide film. Particularly, since the growth rate of the silicon oxide film around the attachment tends to be accelerated, a silicon oxide film is formed as if the attachment is attracted.

The forced oxidation time by the ozone gas is not particularly limited, but a more sufficient silicon oxide film can be formed by setting it to 1 minute or more. More preferably 3 minutes or more.

The forced oxidation by the ozone gas is preferably performed while continuously supplying the ozone gas in the closed container. However, the present invention is not limited to this, and even if a method of directly spraying the ozone gas on the surface of the silicon wafer in the opened container is used The same effect can be obtained.

The forced oxidation is not limited to the ozone gas, and the same effect can be obtained by the ozonated water.

As described above, any one of ozone gas and ozone water may be used, and it is more preferable to use ozone gas to spread easily due to minute scratches or the like.

Thereafter, immersion or a hydrofluoric acid aqueous solution is injected into the aqueous solution of hydrofluoric acid, and the adhered substances of metal impurities are removed together with the silicon oxide grown on the surface layer of the silicon wafer by forced oxidation.

Further, the same effect can be obtained not only by the hydrofluoric acid aqueous solution but also by the hydrofluoric acid vapor.

As described above, any one of an aqueous solution of hydrofluoric acid and a hydrofluoric acid vapor may be used. It is more preferable that the aqueous solution of hydrofluoric acid is sprayed onto the surface of the silicon wafer, considering that the metal impurities are removed from the surface of the wafer and discharged to the outside of the system.

<RCA cleaning, pure cleaning>

After the metal impurity removal treatment as described above, rinsing with pure water is performed. In order to prevent the adhesion of environmental particles in the air, it is more preferably put into the finishing polishing of the next step while being submerged.

Alternatively, the metal impurity removal treatment may be performed, then the RCA cleaning may be performed, and then rinsing with pure water may be performed. By doing so, the particles on the surface of the silicon wafer can be further removed, and then the finish polishing to be performed can be performed.

<Finishing Polishing>

Followed by finish polishing. In the finish polishing, a sufficient amount of cutting is ensured to sufficiently remove the depth of residual scratches and micro cracks. The amount of cutting at this time is not particularly limited and varies depending on the process up to now, and is preferably 10 nm or more.

Various conditions such as the polishing apparatus to be used, the composition of the polishing slurry, the temperature, the polishing pressure, the polishing rate, and the polishing rate are not particularly limited, and any of the conventional conditions can be adopted and can be determined each time.

<Finishing cleaning>

After finishing polishing, finishing cleaning is performed. The method of finishing cleaning is not particularly limited and can be appropriately determined. Here, RCA cleaning and pure cleaning were performed. Any cleaning method capable of removing various particles present on the surface of the wafer after finish polishing can be used.

In the present invention, since the metal impurities on the surface of the silicon wafer are removed before the finish polishing, there is no difference in hardness between the silicon and the metal on the surface of the silicon wafer, which is a cause of the PID in the finish polishing. Therefore, after the finish polishing, the number of PIDs is extremely suppressed, and the surface is finely polished uniformly, so that a polished wafer of flat and high quality can be obtained.

After the mirror polishing process, there is no need to perform cleaning as in Patent Document 2, no concave shape on the surface is generated, and a polished wafer having excellent surface quality can be obtained by the polishing method of the present invention.

(Epitaxial growth step)

Then, an epitaxial layer is formed on the silicon wafer subjected to the mirror polishing process as described above.

The method of forming the epitaxial layer itself is not particularly limited, and for example, the same method as the conventional method can be used.

The epitaxial placing a silicon wafer in the epitaxial growth apparatus, for example, silicon compound gas in the H ₂ atmosphere, SiCl _4, SiHCl _3, SiH ₂ Cl _2, the B ₂ H ₆ gas, PH ₃ gas and dopant gas of SiH light ₄ The epitaxial layer can be laminated in the temperature range of 1000 to 1300 캜.

In the present invention, since the surface of the silicon wafer to be formed with the epitaxial layer is subjected to the mirror polishing process as described above, no PID is present and accordingly even if an epitaxial layer is formed, , Generation of protrusions due to PIDs as in the prior art is largely suppressed. Thus, an epitaxial wafer excellent in surface quality can be obtained.

[Example]

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(Example)

A polishing method of a silicon wafer of the present invention and a manufacturing method of an epitaxial wafer were carried out.

As shown in Fig. 1, a CZ silicon ingot was cut into a wafer by a wire saw, and three silicon wafers among them were subjected to a grinding process to perform RCA cleaning. Thereafter, a mirror polishing process was performed. Further, a silicon wafer having a diameter of 300 mm and a crystal orientation of < 100 > was used.

In the mirror polishing process, first, coarse annealing was performed, and then RCA cleaning, pure cleaning, hydrofluoric acid treatment, and pure cleaning were performed in order to obtain a silicon wafer after rough polishing.

The conditions of the rough polishing (primary polishing and secondary polishing) are as follows.

First, as a pretreatment, a silicon wafer subjected to a grinding and lapping step was etched by 20 탆 with NaOH.

Next, in the double-side polishing apparatus, the both surfaces of the silicon wafer were subjected to primary polishing with an alkali solution of an alkali solution containing colloidal silica as a main component. An abrasion amount of at least 10 탆 can be obtained, and here, the abrasion amount is set at 10 탆. Foamed urethane was used as the polishing cloth.

Next, in the single-side polishing apparatus, secondary polishing of about 1 μm in polishing amount was carried out by using the polishing cloth of polyurethane nonwoven fabric and the polishing agent of colloidal silica of NaOH base in the same manner.

Then, the silicon wafer after the rough polishing was subjected to metal impurity removal treatment. Here, first, a silicon wafer is placed in a container, and an ozone gas is continuously supplied into the container, and the surface of the silicon wafer is oxidized by the ozone gas. The forced oxidation time by the ozone gas was set to 3 minutes.

Subsequently, a 1% aqueous solution of hydrofluoric acid was prepared and sprayed onto the surface of the silicon wafer for 1 minute to remove the metal impurities attached to the surface of the silicon wafer with the silicon oxide film.

As the oxide film removing treatment, the above-mentioned one-minute spraying treatment was performed twice in total.

Thereafter, pure cleaning was performed.

Thereafter, finishing polishing was performed. In this finish polishing, the abrasive cutting amount was used as a control standard and a sufficient abrasion amount was secured to ensure a cutting amount of 80 nm or more. After finishing polishing, RCA cleaning and pure cleaning were carried out to obtain a polished wafer.

Other conditions of the finish polishing are as follows.

In the single-side polishing apparatus, finish polishing was carried out by using a polyurethane suede polishing cloth and an NH ₄ OH -based colloidal silica polishing compound.

The polishing rate was 10 nm / min or less, and the polishing time was 2.5 minutes.

An epitaxial layer was formed on the surface of the polished wafer thus obtained. With the introduction of the silicon compound is SiCl ₄ gas in the polished wafer wit, and H ₂ atmosphere in the epitaxial growth apparatus, the vapor phase growth was 3μm thickness of the epitaxial layer at 1130 ℃.

Thus, an epitaxial wafer was obtained.

(Comparative Example)

Conventional polishing methods for silicon wafers and methods for producing epitaxial wafers were carried out. More specifically, a silicon wafer was polished in the same manner as in Example except that the metal impurity removal step was not performed, to obtain a polished wafer having a diameter of 300 mm and a crystal orientation of < 100 >.

Then, an epitaxial layer was vapor-grown on the polished wafer under the same conditions as in Example to obtain an epitaxial wafer.

Here, the silicon wafer, the polished wafer, and the epitaxial wafer after the rough polishing obtained in the examples and the comparative examples were subjected to surface inspection of the silicon wafer by a laser microscope (MAGICS manufactured by Lasertec Corporation), and the number of defects And to what extent they are reduced in the process.

The result of the surface inspection is shown in Fig. The points in the silicon wafer of Fig. 2 indicate defects (PID, etc.). As shown in Fig. 2, the number of defects in the examples was 1080, 26, and 7 in the silicon wafer, the polished wafer, and the epitaxial wafer after rough polishing. The number of defects in the comparative example was 1279, 585, and 225, respectively.

In the comparative example, the number of defects of the polished wafers after the finish polishing was reduced to about 45% after the rough polishing, whereas in the embodiment of the present invention, it was reduced to about 3%.

Further, the number of defects after epitaxial growth is reduced to about 18% in the comparative example, and to about 0.65% in the embodiment. In the embodiment, the effect of 27 times or more as compared with the comparative example is obtained.

As described above, in the present invention, the number of defects can be significantly reduced, including the PID, compared with the conventional method.

The present invention is not limited to the above-described embodiments. The above-described embodiments are illustrative, and any of those having substantially the same structure as the technical idea described in the claims of the present invention and exhibiting the same operational effects are included in the technical scope of the present invention.

Claims (5)

1. A polishing method for a silicon wafer which performs a mirror polishing process on a silicon wafer,
In the mirror polishing step, abrasion is performed on the silicon wafer, and thereafter, with respect to the surface of the silicon wafer,
Characterized by carrying out a treatment for removing metal impurities adhering to the surface of the silicon wafer by an oxidation treatment using ozone gas or ozone water and an oxide film removal treatment using a hydrofluoric acid vapor or an aqueous solution of hydrofluoric acid, / RTI &gt;
The method according to claim 1,
Wherein the RCA cleaning is performed on the silicon wafer subjected to the metal impurity removal treatment.
The method according to claim 1,
Wherein the finishing cleaning is performed on the silicon wafer subjected to the finishing polishing.
3. The method of claim 2,
Wherein the finishing cleaning is performed on the silicon wafer subjected to the finishing polishing.
A method for manufacturing an epitaxial wafer, characterized in that an epitaxial layer is formed on a surface of a silicon wafer subjected to a mirror polishing process by a polishing method for a silicon wafer according to any one of claims 1 to 4.

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